Troubleshooting One-Lung Ventilation

Abstract

Despite more reliable methods to ensure lung isolation, hypoxia during one-lung ventilation (OLV) can still be a challenge for the anesthesiologist. While a true lower acceptable limit of saturation has not been defined, and is likely different for different patients, cerebral oxygenation does fall significantly during thoracic anesthesia cases, and decreased cerebral oxygenation has been associated with adverse outcomes. Different management strategies can be employed to prevent and treat hypoxia during OLV. These include optimal ventilatory management of the dependent lung, techniques to deliver oxygen to the non-ventilated lung, regulation of physiologic parameters such as circulation, and control of pharmacological factors. This chapter will also cover the issue of the inadequately deflating lung that the anesthesiologist may have to deal with from time to time. A case discussion will follow.

Keywords

Case Discussion

Your next patient is a 65 year-old man awaiting a VATS right upper lobectomy for adenocarcinoma of the lung. He is 169 cm tall and weighs 74.0 kg. He has a preoperative FEV1 of 82% predicted with an obstructive FEV1/FVC ratio and a DLCO of 58%. He quit smoking 3 years ago and is on an ACE inhibitor for hypertension but has no other comorbidities. He climbs two flights of stairs without difficulty.

After a smooth induction and placement of your 39 Fr DLT, you turn the patient on his left side. Because of the obstructive lung disease, you isolate the lung early and pass a suction catheter down the tracheal lumen at 20 cm H2O to encourage lung deflation. The ventilator is set at 15 × 380 with a PEEP of 5, and FiO2 has been turned down to 80%. The surgery begins, and the surgeon is pleased with lung collapse. After 5 min, you notice that the saturation has fallen gradually and is now hovering at 87%.

1.

Is this desaturation surprising in this case?

Early after lung isolation, desaturation may happen because of either tube malposition or because of the slow onset of HPV which has not kicked in fully yet. In this case risk factors include the fact that surgery is taking place on the right lung which implies a potentially larger shunt, and the poor preoperative DLCO which suggests that the PaO2 prior to OLV may already be suboptimal. The patient is also taking a systemic vasodilator drug that can impair HPV.

2.

Describe your management at this point.

The FiO2 and flows should be turned up in order to deliver 100% oxygen. If it appears that the saturation is falling precipitously, it would be prudent to notify the surgeon and resume TLV. Since the fall described here is gradual, bronchoscopy may be performed to confirm adequate tube positioning, and a stepwise approach to hypoxia on one lung can be performed.

3.

The blue cuff is situated well beyond the carina but when scoping down the bronchial lumen, you note that you cannot see the left upper lobe bronchus suggesting that the tube is too far. A larger shunt is likely the cause of the hypoxia because of complete or partial exclusion of the left upper lobe which is not being ventilated due to malpositioning of the tube. You reposition the tube under bronchoscopic guidance by entering the tracheal lumen, pulling the tube back and then confirming through the bronchial lumen that the tip is well situated in the left main bronchus. What do you do next?

Prior to resuming ventilation to the dependent lung, a manual recruitment maneuver may be performed with a gentle sustained pressure of 30 cm H2O for 10 s, as the poorly ventilated left upper lobe has likely developed some atelectasis during this time. You may then proceed to titrate your FiO2 down to aim for a saturation of 92–96%.

4.

The saturation improves to 96% but 10 min later has drifted down again to 88%. Bronchoscopy confirms that the DLT is well positioned. How do you proceed?

Initial steps may include ruling out physiologic derangements that would impair saturation such as decreased perfusion or inadequate or over-ventilation. You may check for hypotension from surgical compression, hypovolemia, or excessive anesthesia and send an ABG to assess PaCO2. An optimal ventilator strategy in the dependent lung is one that avoids the development of atelectasis but doesn’t over distend alveoli to the point that PVR increases in that lung. Following another manual recruitment maneuver, a PEEP decrement trial may be employed, searching for the PEEP that provides optimal compliance. If more than one MAC of volatile is being used, a balanced technique should be employed, or TIVA may be considered if it is not possible to reduce the dose of volatile.

If the saturation has not improved, the surgeon should be made aware and a plan agreed upon. As this case is a VATS, the surgeon will likely be very reluctant to employ CPAP to the non-ventilated lung. They may in fact prefer intermittent gentle re-expansion with 100% oxygen, repeating as needed. An alternate approach would be using a bronchoscope with oxygen attached to the suction port to selectively insufflate the lower lobe segments. This needs to be done in collaboration with the surgeons who can direct their cameras to observe the insufflated segment and avoid overdistension.